guanosine-triphosphate and Dehydration

The cholera vibrio, unlike most pathogens, neither invades the body's cells nor causes them direct physical damage and thus does not engender inflammation or fever. Rather, the organism attaches itself to the intestinal epithelium, where it secretes a toxin that deranges cellular function. Study of the toxin's structure and mechanism of action is helping to elucidate normal enzymatic processes.

Topics: Adenylyl Cyclases; Bacterial Toxins; Cholera; Cholera Toxin; Cyclic AMP; Dehydration; Epithelium; Escherichia coli; Gangliosides; Guanosine Triphosphate; Humans; Intestinal Mucosa; NAD; Structure-Activity Relationship; Water-Electrolyte Imbalance

Blood respiratory properties have been studied in awake and estivating African lungfish, Protopterus amphibius. Fish had been estivating 28-30 months when blood was sampled. Hematocrit, O2 capacity and blood hemoglobin concentration increased by about 50% during estivation. Red cell Hb concentration (MCHC) was unaltered. Total blood concentration of nucleoside triphosphates (NTP) was reduced 50% in estivation. Thin-layer chromatography showed that the change in NTP resulted from a GTP/Hb (guanosine triphosphate) reduction to 20% of the value in awake fish. ATP (adenosine triphosphate) concentration remained largely unaltered. GTP/Hb changes were accompanied by marked changes in O2 affinity. The P50 value in blood from awake fish was 33 mm Hg at pH 7.5 compared to 9 mm Hg for the estivating fish. The n-value changed insignificantly. An increased Bohr effect was present in estivating fish, but its importance will depend on circulating pH in the two states. Standard bicarbonate ranged from a low of 8.6 mMol-L-1 (P plasma) at pH 7.5 in an awake fish to 49.6 mMol-L-1 (P) in an estivating fish. CO2 dissociation curves showed a variable Haldane effect having its highest value in the in vivo range of PCO2. The striking increase in O2-Hb affinity during estivation is regarded as an adaptation to a reduced alveolar O2 availability associated with estivation. Altered mechanics of pulmonary ventilation and reduced ambient O2 availability caused by the subterranean habitat may have been selection pressures for the development of the high O2 availability caused by the subterranean habitat may have been selection pressures for the development of the high O2 affinity. The mechanism behind it rests with the recorded change in erythrocytic concentration of GTP.

Topics: Adaptation, Physiological; Adenosine Triphosphate; Animals; Carbon Dioxide; Dehydration; Estivation; Fishes; Guanosine Triphosphate; Hemoglobins; Oxygen